3GPP LTE-Advanced which is an evolved version of LTE is studying Carrier-Aggregation that performs transmission/reception by bundling a plurality of LTE bands to realize faster transmission (e.g., see Non-Patent Literature 1). LTE terminals detect whether or not a downlink data channel (PDSCH) signal has been received without errors and transmit a response signal thereof (ACK/NACK) to a base station using an uplink control channel (PUCCH). An ACK/NACK transmission method considered in the case of Carrier-Aggregation will be described using FIG. 1.
A terminal individually receives downlink data (PDSCH) for each component band and performs error detection on each piece of data. The terminal transmits the error detection result (response signal) to the base station in an uplink component band corresponding to a downlink component band used to transmit the downlink data through PUCCH. In such a case, when a response signal of each component band is individually transmitted in each uplink component band (Non-Bundling), there is a problem that a single-carrier characteristic collapses, that is, a problem that the amount of interference in PUCCH increases. In order to solve these problems, a response signal transmission method (bundling) is available which bundles a plurality of response signals into one piece by ANDing the plurality of response signals (“1” in the case of ACK and “0” in the case of NACK) and transmits the bundled response signal. However, since the plurality of response signals are ANDed in bundling, if even one NACK is included, the base station recognizes that responses of all bundled data are NACKs and retransmits all the data, resulting in a problem of throughput degradation.
The above-described component band may be defined by a physical cell number and a carrier frequency number, and the component band is sometimes called “cell.”